a. Field of the Invention
This invention relates to a strip lighting device and to a pointer for a display including such a strip lighting device. More particularly this invention relates to a strip lighting device for use in a pointer of a motor vehicle display.
b. Related Art
Light pipes or light guides are known for use in the illumination of moving pointers in displays and also for the static illumination of display surfaces or other features. These light pipes find particular use in motor vehicle dashboard displays. All such elongate or slender illuminated devices are referred to herein as strip lighting devices.
The light pipes are typically made of a transparent or translucent plastics material, and utilize the principle of total internal reflection occurring at the material/air interface to obtain transmission of light along the light pipe.
In many applications it is desirable to extract light along the length of the light pipe, either in discrete regions or continuously along its length. Various extracting features are known in the art, for example a rough surface finish or notches formed in the surface of the light pipe, which are used to introduce losses in that region of the light pipe.
While the use of these known extracting features can be an effective and simple mechanism for creating the desired illumination in some circumstances, there are situations in which it is not possible or desirable to include the extraction features, thereby limiting the control of light output along the length of the light pipe. In motor vehicles, the light pipes used as halo rings around the headlights and the light pipes used in the dashboard display, for example in a pointer, are visible and the appearance and shape of the light pipe is entirely defined by styling of that vehicle. As such, it is not possible to modify the appearance of the light pipe through the introduction of extracting features, for example surface texturing, to enable the amount of light extracted from the light pipe to be controlled. In these situations, therefore, illumination intensity along and around the light pipe depends largely on the styling imposed by the car manufacturer and the end customer.
One particular example is a light pipe used within the arm of a moving pointer in a dashboard display (e.g. speedometer). It can be difficult to achieve an even intensity of illumination along the pointer and, typically, the illumination varies significantly between the root and the tip of the pointer arm. Furthermore, customer feedback is creating increased demands on the required uniformity of the illumination of the pointers, to improve the ease with which the displays are read and to improve the overall appearance of the display. The use of current methods and extraction features, however, typically cannot achieve an illumination intensity variation along a pointer arm of less than 10%, without noticeably affecting the appearance of the pointer arm.
It is, therefore, an object of the present invention to provide an improved strip lighting device incorporating a light guide, including means for controlling the amount of light extracted from the light guide that overcomes some of the drawbacks described above.